Method and system for wavelength division multiplexed optical signal transmission and optical repeater

ABSTRACT

A wavelength division multiplexed optical signal transmission method, a wavelength division multiplexed optical signal transmission system and an optical repeater enabling the number of wavelengths to be detected without error even when optical noise is caused in the optical repeater and such functions as adjustment and monitoring of the level of a wavelength division multiplexed optical signal to be performed properly. An optical repeater processes controlled optical signals of different wavelengths individually based on a control optical signal that contains wavelength number information indicating the total number of wavelengths and the presence or absence of a controlled optical signal with respect to each wavelength. Thus, even when optical noise is caused in the optical repeater, the number of wavelengths can be detected without error and such functions as adjustment and monitoring of the level of a wavelength division multiplexed optical signal can be performed properly.

FIELD OF THE INVENTION

The present invention relates to a wavelength division multiplexedoptical signal transmission method, a wavelength division multiplexedoptical signal transmission system, and an optical repeater.

BACKGROUND OF THE INVENTION

A description will be given of a conventional wavelength divisionmultiplexed (hereinafter referred to as WDM) optical signal transmissionsystem with reference to FIG. 1.

As shown in FIG. 1, the conventional WDM optical signal transmissionsystem comprises a wavelength multiplexer 100 as an upstream device, anoptical repeater 900, and a wavelength demultiplexer 102 as a downstreamdevice. The WDM optical signal transmission system is provided withoptical fibers 7-1 and 7-2 in the route from the wavelength multiplexer100 to the wavelength demultiplexer 102 to transmit WDM optical signals.

There may be disposed a plurality of the optical repeaters 900 dependingon the length of a transmission line or the attenuation in the level ofa received optical signal. The optical repeater 900 is capable ofdiverting an arbitrary optical signal to an external interface as wellas wavelength multiplexing optical signals newly received from theexternal interface.

In FIG. 1 illustrating the wavelength multiplexer 100, optical repeater900, and wavelength demultiplexer 102, the reference numeral 1-1represents external interface signal receiving sections. Each of theexternal interface signal receiving sections 1-1 receives an opticalsignal from an opposite device and converts it to a signal having anarbitrary wavelength. Any device may serve as the opposite device solong as it deals with signals that can be interfaced with the externalinterface signal receiving section 1-1 and an external interface signaltransmitting section 6-1. Examples of the opposite device include an STM(Synchronous Transfer Mode) transmitter dealing with STM signals, an ATM(Asynchronous Transfer Mode) transmitter, and a router dealing withgigabit signals on the Internet, etc. The wavelength multiplexer anddemultiplexer may constitute opposite devices. The wavelengthmultiplexer and demultiplexer do not controls respective interfacesignals and restore their wavelengths to their original conditions whenoutputting them. The reference numerals 2-1 and 2-2 represent wavelengthmultiplexing sections. Having received optical signals of n wavelengthsλ1 to λn obtained by the external interface signal receiving sections1-1, the wavelength multiplexing section 2-1 or 2-2 generates a WDMoptical signal and adjust the optical level according to the number ofthe wavelengths to send it to the transmission line. Further, thereference numerals 3, 3-1 and 3-3 represent wavelength numberinformation managing sections for managing the number of wavelengths ofoptical signals wavelength multiplexed into a WDM optical signal.

“The number of wavelengths” (also referred to as the total number ofwavelengths) herein indicates the number of optical signals multiplexedinto a WDM optical signal. For example, when 16 optical signals aremultiplexed, optical signals of 16 different wavelengths aremultiplexed. Similarly, when 40 optical signals are multiplexed, opticalsignals of 40 different wavelengths are multiplexed. Besides,“wavelength” sometimes indicates each of optical signals multiplexedinto a WDM optical signal. Respective optical signals are converted tosignals having arbitrary wavelengths, and there exist no optical signalshaving the same wavelength. Further, “transmission” does not mean radiotransmission, but it means the transmission of electrical signalsthrough an internal bus or the transmission of a WDM signal through anoptical fiber.

The reference numerals 4-1 and 4-2 represent wavelength demultiplexingsections. Having received a WDM optical signal from the transmissionline, the wavelength demultiplexing section 4-1 or 4-2 adjusts theoptical level according to the number of the wavelengths anddemultiplexes the signal into signals having different wavelengths. Thereference numeral 5-1 represents wavelength repeating sections forcompensating a deteriorated signal to restore it to its originalquality. The reference numeral 6-1 represents an external interfacesignal transmitting section. The external interface signal transmittingsection 6-1 transmits a signal to an opposite device. The referencenumerals S1 and S2 represent WDM optical signals.

In, for example, Japanese Patent Applications laid open No. HEI10-303823and No. 2001-7829, there have been described techniques for transmittinginformation on the number of wavelengths with such devices as thewavelength multiplexer 100, optical repeater 900, and wavelengthdemultiplexer 102.

The conventional techniques, however, have the following problems.

The first problem is that, the information on the number of wavelengths(hereinafter referred to as wavelength number information), which issent from the wavelength multiplexer to the optical repeater, indicatesonly the total number of wavelengths. Besides, the wavelength numberinformation is simply created based on input levels in each singledevice regardless of settings for respective wavelengths.

The second problem is that, when a plurality of optical repeaters areconnected in series as shown in FIG. 2, or intervals between wavelengthsto be multiplexed are narrow, an error occurs in detection.

FIG. 2 is a diagram showing a plurality of optical repeaters connectedin series.

Particularly, in such a system, with a plurality of optical repeaters900-1, 900-2, . . . , 900-n being connected in series, as shown in FIG.2, an error easily occurs in detection. Therefore, a system capable ofpreventing erroneous detection is desired.

FIG. 3(a) is a diagram showing the row of wavelengths to be multiplexed.FIG. 3(b) is a diagram showing a part depicted in FIG. 3(a) on largerscale. In both the drawings, the horizontal axis indicates wavelength(nm) while the vertical axis indicates optical signal level (dB).

As can be seen in FIG. 3(b), in the case of the system comprising aplurality of the optical repeaters connected in series, the waveform ofa WDM optical signal distorts as indicated by the dotted line N, whichcauses optical noise in a WDM optical signal. Provided that theintensity of optical noise is Ln, an increase in Ln causes a falserepresentation of an optical signal with a wavelength (λX in FIG. 3(b)),at which originally no signal is present, when a WDM optical signal isdemultiplexed. Thus, the number of wavelengths may be erroneouslydetected.

That is, according to the conventional techniques, since the wavelengthnumber information is created based on only the presence or absence ofoptical signals to be wavelength multiplexed, the number of wavelengthsis erroneously detected when optical noise is caused in the opticalrepeater. Consequently, such functions as adjustment and monitoring ofthe level of a WDM optical signal can be performed erroneously orunusually.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide awavelength division multiplexed optical signal transmission method, awavelength division multiplexed optical signal transmission system, andan optical repeater for detecting the number of wavelengths withouterror even when optical noise is caused in an optical repeater as wellas performing such functions as adjustment and monitoring of the levelof a wavelength division multiplexed optical signal properly.

In accordance with the first aspect of the present invention, to achievethe object mentioned above, there is provided a wavelength divisionmultiplexed optical signal transmission method for transmitting via oneor more optical repeaters a wavelength division multiplexed opticalsignal composed of a control optical signal and a plurality ofcontrolled optical signals from an upstream device to a downstreamdevice through optical fibers, the method comprising the steps of:

in the optical repeater, demultiplexing a wavelength divisionmultiplexed optical signal transmitted from the upstream device intooptical signals each having a different wavelength;

processing the controlled optical signals of different wavelengthsindividually based on the control optical signal that containswavelength number information indicating the presence or absence of acontrolled optical signal with respect to each wavelength;

remultiplexing the control optical signal and the controlled opticalsignals that have undergone the processing to obtain a wavelengthdivision multiplexed optical signal; and

transmitting the wavelength division multiplexed optical signal to thedownstream device.

In accordance with the second aspect of the present invention, there isprovided a wavelength division multiplexed optical signal transmissionmethod in which a plurality of optical repeaters connected in a ring byoptical fibers transmit a wavelength division multiplexed optical signalcomposed of a control optical signal and a plurality of controlledoptical signals from one to another in one direction, the methodcomprising the steps of:

in the optical repeater, demultiplexing a wavelength divisionmultiplexed optical signal transmitted from an upstream optical repeaterinto optical signals each having a different wavelength;

processing the controlled optical signals of different wavelengthsindividually based on the control optical signal that containswavelength number information indicating the presence or absence of acontrolled optical signal with respect to each wavelength;

remultiplexing the control optical signal and the controlled opticalsignals that have undergone the processing to obtain a wavelengthdivision multiplexed optical signal; and

transmitting the wavelength division multiplexed optical signal to adownstream optical repeater.

In accordance with the third aspect of the present invention, there isprovided a wavelength division multiplexed optical signal transmissionmethod for transmitting wavelength division multiplexed optical signalseach composed of a control optical signal and a plurality of controlledoptical signals in opposite directions through transmission lines by aplurality of optical repeaters each having a pair of optical repeaterunits, ones of the repeater unit pairs in the respective opticalrepeaters being connected by optical fibers to form a ring transmissionline and the others also being connected by optical fibers to form aring transmission line, or ones of the repeater unit pairs in therespective optical repeaters being connected by optical fibers to form astraight transmission line, the others also being connected by opticalfibers to form a straight transmission line and optical repeater unitsat both ends being connected to an upstream device and a downstreamdevice, respectively, the method comprising the steps of:

in the optical repeater unit, demultiplexing a wavelength divisionmultiplexed optical signal transmitted from an upstream optical repeaterunit into optical signals each having a different wavelength;

processing the controlled optical signals of different wavelengthsindividually based on the control optical signal that containswavelength number information indicating the presence or absence of acontrolled optical signal with respect to each wavelength;

remultiplexing the control optical signal and the controlled opticalsignals that have undergone the processing to obtain a wavelengthdivision multiplexed optical signal; and

transmitting the wavelength division multiplexed optical signal to adownstream optical repeater unit.

In accordance with the fourth aspect of the present invention, there isprovided a wavelength division multiplexed optical signal transmissionsystem comprising an upstream device, one or more optical repeaters anda downstream device for transmitting via the optical repeater awavelength division multiplexed optical signal composed of a controloptical signal and a plurality of controlled optical signals from theupstream device to the downstream device through optical fibers,wherein:

the upstream device includes a receiver for receiving a control opticalsignal and controlled optical signals and a multiplexer for multiplexingthe control optical signal and the controlled optical signals receivedby the receiver;

the optical repeater includes a demultiplexer for demultiplexing awavelength division multiplexed optical signal transmitted from theupstream device into optical signals each having a different wavelength,a processor for processing the controlled optical signals of differentwavelengths individually based on the control optical signal thatcontains wavelength number information indicating the presence orabsence of a controlled optical signal with respect to each wavelength,and a multiplexer for remultiplexing the control optical signal and thecontrolled optical signals; and

the downstream device includes a demultiplexer for demultiplexing awavelength division multiplexed optical signal transmitted from theoptical repeater and a transmitter for transmitting a control opticalsignal and controlled optical signals obtained by demultiplexing thewavelength division multiplexed optical signal to the outside.

In accordance with the fifth aspect of the present invention, there isprovided a wavelength division multiplexed optical signal transmissionsystem comprising a plurality of optical repeaters connected in a ringby optical fibers which transmit a wavelength division multiplexedoptical signal composed of a control optical signal and a plurality ofcontrolled optical signals from one to another in one direction, whereinthe optical repeater includes a demultiplexer for demultiplexing awavelength division multiplexed optical signal transmitted from anupstream optical repeater into optical signals each having a differentwavelength, a processor for processing the controlled optical signals ofdifferent wavelengths individually based on the control optical signalthat contains wavelength number information indicating the presence orabsence of a controlled optical signal with respect to each wavelength,and a multiplexer for remultiplexing the control optical signal and thecontrolled optical signals to transmit a wavelength division multiplexedoptical signal to a downstream optical repeater.

In accordance with the sixth aspect of the present invention, there isprovided a wavelength division multiplexed optical signal transmissionsystem comprising a plurality of optical repeaters each having a pair ofoptical repeater units which transmit wavelength division multiplexedoptical signals each composed of a control optical signal and aplurality of controlled optical signals in opposite directions throughtransmission lines, wherein:

ones of the repeater unit pairs in the respective optical repeaters areconnected by optical fibers to form a ring transmission line, and theothers are also connected by optical fibers to form a ring transmissionline; or

ones of the repeater unit pairs in the respective optical repeaters areconnected by optical fibers to form a straight transmission line, theothers are also connected by optical fibers to form a straighttransmission line, and optical repeater units at both ends are connectedto an upstream device and a downstream device, respectively; and

the optical repeater unit includes a demultiplexer for demultiplexing awavelength division multiplexed optical signal transmitted from anupstream optical repeater unit into optical signals each having adifferent wavelength, a processor for processing the controlled opticalsignals of different wavelengths individually based on the controloptical signal that contains wavelength number information indicatingthe presence or absence of a controlled optical signal with respect toeach wavelength, and a multiplexer for remultiplexing the controloptical signal and the controlled optical signals that have undergonethe processing by the processor.

In accordance with the seventh aspect of the present invention, there isprovided an optical repeater for transmitting a wavelength divisionmultiplexed optical signal composed of a control optical signal and aplurality of controlled optical signals from the upstream device to thedownstream device through optical fibers, the optical repeatercomprising:

a demultiplexer for demultiplexing a wavelength division multiplexedoptical signal transmitted from the upstream device into optical signalseach having a different wavelength;

a processor for processing the controlled optical signals of differentwavelengths individually based on the control optical signal thatcontains wavelength number information indicating the presence orabsence of a controlled optical signal with respect to each wavelength;and

a multiplexer for remultiplexing the control optical signal and thecontrolled optical signals.

In accordance with the eighth aspect of the present invention, there isprovided an optical repeater applied to a wavelength divisionmultiplexed optical signal transmission system comprising a plurality ofthe optical repeaters connected in a ring by optical fibers whichtransmit a wavelength division multiplexed optical signal composed of acontrol optical signal and a plurality of controlled optical signalsfrom one to another in one direction, the optical repeater comprising:

a demultiplexer for demultiplexing a wavelength division multiplexedoptical signal transmitted from an upstream optical repeater intooptical signals each having a different wavelength;

a processor for processing the controlled optical signals of differentwavelengths individually based on the control optical signal thatcontains wavelength number information indicating the presence orabsence of a controlled optical signal with respect to each wavelength;and

a multiplexer for remultiplexing the control optical signal and thecontrolled optical signals to transmit a wavelength division multiplexedoptical signal to a downstream optical repeater.

In accordance with the ninth aspect of the present invention, there isprovided an optical repeater applied to a wavelength divisionmultiplexed optical signal transmission system comprising a plurality ofthe optical repeaters each having a pair of optical repeater units whichtransmit wavelength division multiplexed optical signals each composedof a control optical signal and a plurality of controlled opticalsignals in opposite directions through transmission lines, wherein:

ones of the repeater unit pairs in the respective optical repeaters areconnected by optical fibers to form a ring transmission line, and theothers are also connected by optical fibers to form a ring transmissionline; or

ones of the repeater unit pairs in the respective optical repeaters areconnected by optical fibers to form a straight transmission line, theothers are also connected by optical fibers to form a straighttransmission line, and optical repeater units at both ends are connectedto an upstream device and a downstream device, respectively; and

the optical repeater unit includes a demultiplexer for demultiplexing awavelength division multiplexed optical signal transmitted from anupstream optical repeater unit into optical signals each having adifferent wavelength, a processor for processing the controlled opticalsignals of different wavelengths individually based on the controloptical signal that contains wavelength number information indicatingthe presence or absence of a controlled optical signal with respect toeach wavelength, and a multiplexer for remultiplexing the controloptical signal and the controlled optical signals that have undergonethe processing by the processor.

In the case where the wavelength number information provides a signalpresent indication corresponding to a controlled optical signal, whenthe signal has not deteriorated, the signal may pass through without achange in the signal present indication of the wavelength numberinformation, while, when the signal has deteriorated, the signal may beonce terminated and regenerated so that a new controlled optical signalregenerated from the signal can pass through without a change in thesignal present indication of the wavelength number information.

On the other hand, in the case where the wavelength number informationprovides a signal absent indication corresponding to a controlledoptical signal, when an optical signal is received from the outside, theoptical signal may be output as the controlled optical signal and thewavelength number information is updated to indicate the presence of thesignal, while, when no optical signal is received from the outside, thecontrolled optical signal is terminated without a change in the signalabsent indication of the wavelength number information.

Besides, functions for adjustment and monitoring of the level of aninput wavelength division multiplexed optical signal may be controlledbased on the wavelength number information from the control opticalsignal.

In addition, the wavelength number information may include informationon the number of multiplexed wavelengths.

BRIEF DESCRIPTION OF THE DRAWINGS

The exemplary aspects and features of the present invention will becomemore apparent from the consideration of the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a diagram showing a wavelength division multiplexed opticalsignal transmission system to which is applied a conventional wavelengthdivision multiplexed optical signal transmission method;

FIG. 2 is a diagram showing a plurality of optical repeaters connectedin series;

FIG. 3(a) is a diagram showing the row of optical signals to bewavelength-division multiplexed;

FIG. 3(b) is a diagram showing a part depicted in FIG. 3(a) on largerscale;

FIG. 4 is a schematic diagram showing a wavelength division multiplexedoptical signal transmission system to which is applied a wavelengthdivision multiplexed optical signal transmission method according to anembodiment of the present invention;

FIG. 5 is a diagram showing a wavelength number information signaltransmitted in the wavelength division multiplexed optical signaltransmission system depicted in FIG. 4;

FIG. 6 is a diagram showing a method of updating wavelength numberinformation in an optical repeater depicted in FIG. 4;

FIG. 7 is a flowchart showing the operation of a wavelength multiplexerdepicted in FIG. 4 for processing a wavelength number informationsignal;

FIG. 8 is a flowchart showing the operation of the optical repeaterdepicted in FIG. 4 for processing a wavelength number informationsignal;

FIG. 9 is a flowchart showing the operation of a wavelengthdemultiplexer depicted in FIG. 4 for processing a wavelength numberinformation signal;

FIG. 10 is a schematic diagram showing a wavelength division multiplexedoptical signal transmission system to which is applied a wavelengthdivision multiplexed optical signal transmission method according toanother embodiment of the present invention;

FIG. 11(a) is a schematic diagram showing a wavelength divisionmultiplexed optical signal transmission system to which is applied awavelength division multiplexed optical signal transmission methodaccording to another embodiment of the present invention;

FIG. 11(b) is a schematic diagram showing an optical repeater depictedin FIG. 11(a); and

FIG. 12 is a schematic diagram showing a wavelength division multiplexedoptical signal transmission system to which is applied a wavelengthdivision multiplexed optical signal transmission method according to yetanother embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, a description of preferred embodiments ofthe present invention will be given in detail.

A wavelength division multiplexed optical signal transmission method, awavelength division multiplexed optical signal transmission system andan optical repeater of the present invention are aimed at correctlyperforming such functions as adjustment and monitoring of the level of awavelength division multiplexed optical signal in a wavelength divisionmultiplexing transmission system. The present invention is characterizedby preventing the generation of incorrect wavelength number informationdue to the erroneous recognition of a signal caused by an abnormaloptical signal level so that wavelength number information indicatingthe number of wavelengths different from that of a multiplexed opticalsignal is not to be transmitted.

FIG. 4 is a schematic diagram showing a wavelength division multiplexedoptical signal transmission system to which is applied a wavelengthdivision multiplexed optical signal transmission method according to anembodiment of the present invention.

Referring to FIG. 4, the WDM (wavelength division multiplexed) opticalsignal transmission system comprises a wavelength multiplexer 100 as anupstream device, an optical repeater 101, and a wavelength demultiplexer102 as a downstream device.

The wavelength multiplexer 100 includes external interface signalreceiving sections 1-1 for receiving controlled optical signals of nwavelengths λ1 to λn, a wavelength multiplexing section 2-1 formultiplexing (wavelength multiplexing) optical signals input from therespective external interface signal receiving sections 1-1, and awavelength number information managing section 3-1 for managing opticalsignals for the wavelength multiplexing section 2-1.

The wavelength number information managing section 3-1 monitors thepresence or absence of a controlled optical signal received in each ofinput sections (ports) P11 to P1 n of the wavelength multiplexingsection 2-1. The wavelength number information managing section 3-1 addswavelength number information indicating the presence or absence ofcontrolled optical signals (wavelength: λ1 to λn) in the respectiveports individually to a control optical signal (wavelength numberinformation signal). Subsequently, the wavelength multiplexing section2-1 multiplexes all controlled optical signals and the control opticalsignal to output a WDM optical signal S1 to one end (left end in thedrawing) of an optical fiber or cable 7-1. That is, the WDM opticalsignal S1 is composed of controlled optical signals of n wavelengths λ1to λn and a wavelength number information signal of wavelength λn+1.Incidentally, the wavelength λn+1 is cited merely by way of example andwithout limitation. The wavelength number information signal may haveany wavelength other than those (wavelengths λ1 to λn) of the controlledoptical signals. From the external interface signal receiving sections1-1 of the wavelength multiplexer 100, the controlled optical signalsare input to the ports P11 to P1 n, respectively, while the controloptical signal is input to the port P1 n+1.

The optical repeater 101 includes a wavelength multiplexing section 2-2,a wavelength number information managing section 3-2, a wavelengthdemultiplexing section 4-1, wavelength repeating sections 5-1 and anexternal interface signal transmitting section 6-1. The input side ofthe wavelength demultiplexing section 4-1 is connected to the other end(right end in the drawing) of the optical fiber 7-1. The wavelengthnumber information managing section 3-2 performs necessary processingfor controlled optical signals according to wavelength numberinformation about the presence or absence of the respective controlledoptical signals in the output sections (ports P21 to P2 n) of thewavelength demultiplexing section 4-1 and the necessity of compensatingthe signals. After the processing, the wavelength number informationmanaging section 3-2 sends the controlled optical signals to the inputsections (ports P31 to P3 n) of the wavelength multiplexing section 2-2as a multiplexer. Having received the optical signals, which haveundergone the processing, through the input sections (ports P31 to P3n), the wavelength multiplexing section 2-2 performs necessaryprocessing based on the wavelength number information from thewavelength number information managing section 3-2, and multiplexes thecontrol optical signal and controlled optical signals which haveundergone the processing to output a WDM optical signal S2 to one end(left end in the drawing) of an optical fiber 7-2.

In FIG. 4, the wavelength repeating section 5-1 is placed between theports P21 and P31, the ports P22 and P23 are directly connected to theports P32 and P33, respectively, the output side of an externalinterface signal receiving section 1-2 as a receiver is connected to theport P34, the output side of the port P25 is connected to the input sideof the external interface signal transmitting section 6-1 as atransmitter, and the port P2 n is directly connected to the port P3 n.However, these connections are not so limited but vary according to theuse conditions or quality of controlled optical signals of a WDM opticalsignal.

The wavelength number information managing section 3-2 includes awavelength number information signal receiving section 32, a receivingside wavelength number information extracting section 33, an externalsetting judging section 35, a transmitting side wavelength numberinformation generating section 37, and a wavelength number informationsignal generating section 39.

The wavelength number information managing section 3-1 of the wavelengthmultiplexer 100 and that (section 3-3) of the wavelength demultiplexer102 have the same construction as described above for the section 3-2.

The wavelength multiplexer 100, optical repeater 101 and wavelengthdemultiplexer 102 perform the process 1 through 9 (the wavelengthmultiplexer 100 performs the process 6 through 8, the optical repeater101 performs the process 1 through 9, and the wavelength demultiplexer102 performs the processs 1 through 3) as follows:

1. the wavelength demultiplexing section separates out a wavelengthnumber information signal 31 received from the upstream device to sendit as an optical signal to the wavelength number information signalreceiving section 32 of the wavelength number information managingsection

2. the wavelength number information signal receiving section 32converts the optical signal received from the wavelength demultiplexingsection into an electrical signal to send it to the receiving sidewavelength number information extracting section 33

3. the receiving side wavelength number information extracting section33 extracts wavelength number information from the wavelength numberinformation signal to inform the wavelength demultiplexing section ofthe total number of wavelengths (receiving side total wavelength numberinformation 34)

4. the receiving side wavelength number information extracting section33 sends information on the presence or absence of optical signals ofrespective wavelengths λ1 to λn to the external setting judging section35

5. the external setting judging section 35 determines whether or not toupdate the information on the presence or absence of optical signals ofrespective wavelengths λ1 to λn based on external settings (“terminate”/“pass”) corresponding to the respective wavelengths λ1 to λn, andinforms the transmitting side wavelength number information generatingsection 37 of the results

6. the transmitting side wavelength number information generatingsection 37 receives information on the presence or absence of opticalsignals of respective wavelengths λ1 to λn (signal present/absentinformation 36) form the wavelength multiplexing section

7. in the wavelength multiplexer 100, the transmitting side wavelengthnumber information generating section 37 generates transmitting sidewavelength number information based on the information obtained in theprocess 6, while in the optical repeater 101, the section 37 generatesit based on the information obtained in the processes 5 and 6

8. the transmitting side wavelength number information generatingsection 37 informs the wavelength multiplexing section of the totalnumber of wavelengths (transmitting side total wavelength numberinformation 38) according to the transmitting side wavelength numberinformation which the section 37 has generated

9. the wavelength number information signal generating section 39receives the transmitting side wavelength number information generatedby the transmitting side wavelength number information generatingsection 37, and converts the electrical signal into an optical signalhaving an arbitrary wavelength to send it to the wavelength multiplexingsection so that the signal is multiplexed together with optical signalsof other wavelengths

In the following, a description will be given of the external settingsused by the external setting judging section 35. The “external setting”is provided to the wavelength multiplexing sections 2-1 and 2-2 by anexternal maintainer (not shown) at the time of line setting to indicatethe condition of a controlled optical signal in each of input sectionsor ports. That is, the external setting indicates that each controlledoptical signal corresponds to one of signals A to C as follows:

A. a signal from one of the external interface signal receiving sections1-1 (including a signal to which a wavelength has not yet been assigned)

B. a controlled optical signal which has passed through the wavelengthrepeating section 5-1

C. a controlled optical signal which is input from the wavelengthdemultiplexing section 4-1 to the wavelength multiplexing section 2-2,not via the wavelength repeating section 5-1

With regard to the signals A and B, since a controlled optical signal isregenerated in each block, optical noise can be eliminated. On the otherhand, in the case of the signal C, a signal is not regenerated afterwavelength demultiplexing, and therefore, it is necessary to takeoptical noise into consideration. Accordingly, there exist two types ofsettings: “termination” corresponding to the signals A and B and “pass”corresponding to the signal C. For example, in a system capable ofmultiplexing controlled optical signals of up to 16 wavelengths, thereare a total of 16 settings, one for each wavelength.

The wavelength demultiplexer 102 as a downstream device controls suchfunctions as adjustment and monitoring of the level of a WDM opticalsignal input thereto based on wavelength number information added to awavelength number information signal separated out in the wavelengthdemultiplexing section 4-2.

As just described, in accordance with the present invention, wavelengthnumber information used in a WDM optical signal transmission systemincludes not only the total number of wavelengths but also the presenceor absence of an optical signal with respect to each wavelength. In theoptical repeater 101, it is determined for each wavelength to directlyuse wavelength number information transmitted from the wavelengthmultiplexer 100, or to newly use information as to whether a controlledoptical signal has been input to the wavelength multiplexing section2-2. Thereby, the optical repeater 101 is prevented from erroneouslydetermining that a signal is “present” due to an abnormal signal levelcaused by optical noise. Thus, the optical repeater 101 informs thewavelength demultiplexer 102 of the correct number of wavelengths, whichenables such functions as adjustment and monitoring of the level of aWDM optical signal to be performed properly.

First Embodiment

FIG. 4 shows a wavelength division multiplexed optical signaltransmission system to which is applied a wavelength divisionmultiplexed optical signal transmission method according to the firstembodiment of the present invention.

As can be seen in FIG. 4, the WDM (wavelength division multiplexed)optical signal transmission system comprises a wavelength multiplexer100, an optical repeater 101, and a wavelength demultiplexer 102. In theWDM optical signal transmission system, WDM optical signals S1 and S2,each obtained by multiplexing controlled optical signals of up to nwavelengths (wavelength: λ1 to λn) and one control optical signal(wavelength: λn+1), are transmitted along the route from the wavelengthmultiplexer 100 to the wavelength demultiplexer 102.

There may be disposed a plurality of the optical repeaters 101 dependingon the length or distance of a transmission line (optical fibers 7-1 and7-2) or the attenuation in the level of a received optical signal. Theoptical repeater 101 is capable of diverting an arbitrary optical signalto an external interface signal transmitting section 6-1 as well aswavelength multiplexing optical signals newly received through anexternal interface signal receiving section 1-2.

In FIG. 4 illustrating the wavelength multiplexer 100, optical repeater101, and wavelength demultiplexer 102, the reference numerals 1-1 and1-2 represent external interface signal receiving sections. Each of theexternal interface signal receiving sections receives an optical signalfrom an opposite device (not shown) and converts it to a controlledoptical signal having an arbitrary wavelength.

The reference numeral 2-1 represents a wavelength multiplexing section.Having received a control optical signal and controlled optical signalsof n different wavelengths obtained in the external interface signalreceiving sections 1-1, the wavelength multiplexing section 2-1generates a WDM optical signal S1 and adjust the optical signal levelaccording to the number of the wavelengths to send it to thetransmission line (optical fiber 7-1).

The reference numeral 2-2 also represents a wavelength multiplexingsection. However, differently from the wavelength multiplexing section2-1, the wavelength multiplexing section 2-2 receives controlled opticalsignals after compensation or regeneration as well as normal controlledoptical signals from a wavelength demultiplexing section 4-1. Further,the wavelength multiplexing section 2-2 receives a controlled opticalsignal obtained in the external interface signal receiving section 1-2.The wavelength multiplexing section 2-2 generates a WDM optical signalS2 with the controlled optical signals and a wavelength numberinformation signal from a wavelength number information managing section3-2 to send it to the transmission line (optical fiber 7-2).

The reference numerals 3-1, 3-2 and 3-3 represent wavelength numberinformation managing sections for managing the number of wavelengths ofthe controlled optical signals multiplexed into the WDM optical signalS1 or S2.

The reference numeral 4-1 represents a wavelength demultiplexingsection. Having received the WDM optical signal S1 from the transmissionline (optical fiber 7-1), the wavelength demultiplexing section 4-1adjusts the optical level of the signal S1 according to the number ofwavelengths and demultiplexes the signal S1 into optical signals ofwavelengths λ1 to λn+1. The wavelength demultiplexing section 4-1outputs the controlled optical signals (wavelength: λ1 to λn) tocorresponding ports P21 to P2 n, respectively, and the control opticalsignal (wavelength: λn+1) to the wavelength number information managingsection 3-2.

The reference numeral 4-2 also represents a wavelength demultiplexingsection. Having received the WDM optical signal S2 from the transmissionline (optical fiber 7-2), the wavelength demultiplexing section 4-2adjusts the optical level of the signal S2 according to the number ofwavelengths and demultiplexes the signal S2 into optical signals ofwavelengths λ1 to λn+1. The wavelength demultiplexing section 4-2outputs the controlled optical signals (wavelength: λ1 to λn) tocorresponding ports P41 to P4 n, respectively, and the control opticalsignal (wavelength: λn+1) to the wavelength number information managingsection 3-3.

The reference numeral 5-1 represents wavelength repeating sections forcompensating a deteriorated controlled optical signal to restore it toits original quality.

The reference numeral 6-1 represents an external interface signaltransmitting section. The external interface signal transmitting section6-1 transmits a controlled optical signal to an opposite device (notshown).

In the wavelength multiplexer 100 shown in FIG. 4, each of opticalsignals received by the external interface signal receiving sections 1-1is converted to an optical signal of an arbitrary wavelength forgenerating a WDM optical signal, and sent to the wavelength multiplexingsection 2-1.

The wavelength multiplexing section 2-1 wavelength multiplexescontrolled optical signals of up to n wavelengths and one controloptical signal to generate the WDM optical signal S1. On this occasion,the input levels of the respective optical signals are monitored atinput sections (ports P11 to P1 n) of the wavelength multiplexingsection 2-1. When the input level is not less than a preset referencevalue, it is determined that the controlled optical signal is “present”.On the other hand, when the input level is less than the referencevalue, it is determined that the controlled optical signal is “absent”.The information is fed to the wavelength number information managingsection 3-1.

The wavelength number information managing section 3-1 generates awavelength number information signal (control optical signal) based onthe wavelength number information received from the wavelengthmultiplexing section 2-1, and sends it to the section 2-1.

The wavelength multiplexing section 2-1 multiplexes controlled opticalsignals of n wavelengths and the wavelength number information signal(control optical signal) to generate the WDM optical signal S1 to sendit to the transmission line (optical fiber 7-1). On this occasion, thewavelength number information managing section 3-1 adjusts the outputlevel of the transmitted optical signal as well as the monitoring levelof the signal level monitoring function according to the number ofwavelengths indicated by the wavelength number information signal.

In the optical repeater 101, the wavelength demultiplexing section 4-1separates the wavelength number information signal (control opticalsignal) from the received WDM optical signal to send it to thewavelength number information managing section 3-2.

The wavelength number information managing section 3-2 feeds thewavelength demultiplexing section 4-1 with information on the totalnumber of wavelengths obtained from the received control optical signal.

When the wavelength demultiplexing section 4-1 demultiplexes thereceived WDM optical signal S1, the control optical signal that containsthe wavelength number information is also subjected to the wavelengthdemultiplexing. At this point, the wavelength demultiplexing section 4-1has not acquired the contents of the control optical signal: thewavelength number information. The wavelength number informationmanaging section 3-2 interprets the contents of the optical signal. Thewavelength demultiplexing section 4-1 needs the wavelength numberinformation concerning the received WDM optical signal S1 to compensatethe level of the optical signal. As the wavelength number information,the wavelength demultiplexing section 4-1 does not use wavelength numberinformation generated in the wavelength number information managingsection 3-2 of its own device but uses information generated in theupstream device. Accordingly, the wavelength number information managingsection 3-2 is required to inform the wavelength demultiplexing section4-1 of the number of wavelengths of the optical signal. The wavelengthdemultiplexing section 4-1 adjusts the level of the received opticalsignal as well as the monitoring level of the signal level monitoringfunction based on the wavelength number information indicated by thecontrol optical signal.

In the wavelength demultiplexing section 4-1, it is determined accordingto settings provided by an external maintainer whether each of opticalsignals (wavelength: λ1 to λn) obtained by wavelength demultiplexing isto be transmitted from the external interface signal transmittingsection 6-1 to the opposite device (not shown) or it is to be sent tothe wavelength multiplexing section 2-2 and remultiplexed into the WDMoptical signal S2.

Line setting regarding from where to where the optical signal istransmitted determines whether each of demultiplexed optical signals isto be sent to the external interface signal transmitting section 6-1 orthe wavelength multiplexing section 2-2.

It is assumed, for example, that the wavelength multiplexer 100 isplaced in the area A, the optical repeater 101 is placed in the area B,and the wavelength demultiplexer 102 is placed in the area C. In thecase of setting a line along the route from the area A to the area B, anoptical signal is sent to the external interface signal transmittingsection 6-1 to be dropped. In the case of setting a line along the routefrom the area A to the area C, an optical signal is sent to thewavelength multiplexing section 2-2. Further, in the case of setting aline along the route from the area B to the area C, an optical signal isnewly sent from the external interface signal receiving section 1-2 tothe wavelength multiplexing section 2-2 to be added.

The “line setting” may be simply provided by the patch connection ofoptical fiber cables connecting respective blocks, or provided by theuse of an optical switch automatically controlled to establish aconnection. It is not necessary for the present invention to specify themethod of implementing the line setting.

Besides, when a signal is remultiplexed into a WDM optical signal, thereis the case where compensation is performed for signal deterioration inthe wavelength repeating section 5-1 depending on transmission distance.

A determination as to whether or not to use the wavelength repeatingsection 5-1 is made based on the transmission distance and the number ofspans between the wavelength multiplexer 100 and the optical repeater101 as well as those between the repeater 101 and the wavelengthdemultiplexer 102. As the transmission distance or the number of spansincreases, a transmitted optical signal deteriorates significantly.Therefore, it is required to regenerate (repeat) the optical signalthrough the use of the wavelength repeating section 5-1. Thetransmission distance that needs signal repeating is uniquely determinedby the distance and the number of spans in which the wavelengthmultiplexer 100, optical repeater 101 and the wavelength demultiplexer102 can assure the quality of a signal without repeating the signal.

In the optical repeater 101, the input levels of controlled opticalsignals are also monitored at input sections (ports P31 to P3 n) of thewavelength multiplexing section 2-2 to determine whether controlledoptical signals of respective wavelengths λ1 to λn are “present” or“absent”. The wavelength multiplexing section 2-2 feeds the wavelengthnumber information managing section 3-2 with the results.

The wavelength number information managing section 3-2 generates awavelength number information signal based on the information receivedfrom the wavelength multiplexing section 2-2 to send it to the section2-2.

The wavelength multiplexing section 2-2 multiplexes the wavelengthnumber information signal together with controlled optical signals of nwavelengths to generate a WDM optical signal to send it to thetransmission line (optical fiber 7-2). On this occasion, the outputlevel of the transmitted optical signal and the monitoring level of thesignal level monitoring function are adjusted according to the number ofwavelengths indicated by the wavelength number information signal.

In the wavelength demultiplexer 102, the wavelength demultiplexingsection 4-2 separates the wavelength number information signal from thereceived WDM optical signal to send it to the wavelength numberinformation managing section 3-3.

The wavelength number information managing section 3-3 feeds thewavelength demultiplexing section 4-2 with information on the number ofwavelengths obtained from the received control optical signal.

Based on the information on the number of wavelengths received from thewavelength number information managing section 3-3, the wavelengthdemultiplexing section 4-2 adjusts the level of the received opticalsignal and the monitoring level of the signal level monitoring function.

The wavelength demultiplexing section 4-2 demultiplexes the WDM opticalsignal into controlled optical signals of respective wavelengths λ1 toλn to transmit them from external interface signal transmitting sections6-2 to opposite devices (not shown).

In the following, a description will be made in detail of the operationof the wavelength multiplexer 100 in the WDM optical signal transmissionsystem of the first embodiment shown in FIG. 4.

The wavelength multiplexing section 2-1 monitors the input levels ofrespective optical signals at the input sections (ports P11 to P1 n) todetermine whether optical signals of respective wavelengths are“present” or “absent”.

In FIG. 4, the optical signal of the first wavelength (port P11) is“present”, the optical signal of the second wavelength (port P12) is“absent”, the optical signal of the third wavelength (port P13) is“present”, the optical signal of the fourth wavelength (port P14) is“absent”, the optical signal of the fifth wavelength (port P15) is“present”, . . . , and the optical signal of the n-th wavelength (portP1 n) is “present”.

The information obtained at the respective input sections (ports P11 toP1 n) is fed to the wavelength number information managing section 3-1.

The wavelength number information managing section 3-1 generates awavelength number information signal based on the information receivedfrom the wavelength multiplexing section 2-1.

FIG. 5 is a diagram showing a wavelength number information signaltransmitted in the WDM optical signal transmission system shown in FIG.4.

Referring to FIG. 5, data D21 indicates the presence or absence of thecontrolled optical signal of the first wavelength, data D22 indicatesthe presence or absence of the controlled optical signal of the secondwavelength, . . . , data D2 n indicates the presence or absence of thecontrolled optical signal of the n-th wavelength, and data D2T indicatesthe total number of wavelengths. The data D21 to D2T provide wavelengthnumber information added to a control optical signal.

A wavelength number information signal has a wavelength different fromthose of optical signals generated in the external interface signalreceiving sections 1-1. The total number of wavelengths is obtained frominformation as to the presence or absence of optical signal input at therespective input sections (ports P11 to P1 n) of the wavelengthmultiplexing section 2-1 and count of the signals present. The totalnumber of wavelengths is stored in the “total wavelength number” area(time slot).

Incidentally, according to the present invention, wavelength numberinformation does not necessarily include the “total wavelength number”.Wavelength number information may include information on the “presence”or “absence” of optical signals of respective wavelengths only. In sucha case, the total number of wavelengths can be figured out in therespective devices by counting optical signals being “present”.

The wavelength multiplexing section 2-1 wavelength multiplexes awavelength number information signal and controlled optical signals ofup to n wavelengths to generate a WDM optical signal, and sends it tothe transmission line (optical fiber 7-1).

In the following, a description will be made in detail of the operationof the optical repeater 101.

The wavelength demultiplexing section 4-1 separates a wavelength numberinformation signal from a received WDM optical signal to send it to thewavelength number information managing section 3-2.

The wavelength number information managing section 3-2 feeds thewavelength demultiplexing section 4-1 with information on the totalnumber of wavelengths obtained from the received optical signal.

The wavelength demultiplexing section 4-1 adjusts the level of opticalsignals that have deteriorated during transmission as well as themonitoring level of the signal level monitoring function based on theinformation as to the total number of wavelengths.

FIG. 6 is a diagram showing the process of updating wavelength numberinformation in the optical repeater 101.

According to settings provided by an external maintainer, adetermination is made as to whether each of controlled optical signals(wavelength: λ1 to λn) obtained by demultiplexing in the wavelengthdemultiplexing section 4-1 is to be transmitted from the externalinterface signal transmitting section 6-1 to the opposite device (notshown) or it is to be sent to the wavelength multiplexing section 2-2and remultiplexed into the WDM optical signal S2.

When an optical signal is transmitted from the external interface signaltransmitting section 6-1 or the wavelength repeating section 5-1 isutilized, the setting provided by an external maintainer indicates“terminate”. On the other hand, when an optical signal is directly sentto the wavelength multiplexing section 2-2, the setting indicates“pass”. In the case where the setting for a wavelength indicates“terminate”, information from the wavelength multiplexing section 2-2becomes effective, and wavelength number information is updated withrespect to the wavelength. On the other hand, in the case where thesetting for a wavelength indicates “pass”, wavelength number informationreceived from the wavelength demultiplexing section 4-1 is directly sentto the wavelength multiplexing section 2-2. However, if wavelengthnumber information sent from the wavelength multiplexing section 2-2indicates the “absence” of an optical signal despite the fact thatwavelength number information from the upstream device indicates the“presence” of the signal, there may be a fault in the route. Therefore,information from the wavelength multiplexing section 2-2 is applied.

Conditions for determining the presence or absence of controlled opticalsignals are shown in table 1 below. TABLE 1 Presence/AbsencePresence/Absence Determination Result of Signal of Signal as toPresence/ Determined Indicated by Absence of from Information fromSignal with Setting Input Level Upstream Device Specific WavelengthTerminate Present Ignored Present Absent Absent Pass Present PresentPresent Absent Absent (Noise) Absent Ignored Absent

A concrete example will be given for purposes of illustration.

The first (top) row shown in FIG. 6 represents wavelength numberinformation from the upstream device (wavelength multiplexer 100). Thewavelength number information includes data D31 indicating the presenceof a controlled optical signal having the first wavelength (λ1), dataD32 indicating the absence of a signal having the second wavelength(λ2), data D33 indicating the presence of a signal having the thirdwavelength (λ3), data D34 indicating the absence of a signal having thefourth wavelength (λ4), . . . , data D3 n indicating the presence of asignal having the n-th wavelength (λn), and data D3T indicating thetotal number “y” of data each indicating the presence of a controlledoptical signal.

In the wavelength number information managing section 3-2, it isdetermined whether or not to update the wavelength number informationshown in the first row based on prescribed settings with respect to eachof the wavelengths λ1 to λn. The data D31 corresponds to setting WS1indicating “terminate”, the data D32 corresponds to setting WS2indicating “pass”, the data D33 corresponds to setting WS3 indicating“pass”, . . . , and the data D3 n corresponds to setting WSn indicating“terminate”.

The third row shown in FIG. 6 represents processing for the wavelengthnumber information to transmit it to the downstream device (wavelengthdemultiplexer 102). The setting WS1 corresponds to data D41 indicating“update”, the setting WS2 corresponds to data D42 indicating the absenceof the controlled optical signal of the second wavelength, the settingWS3 corresponds to data D43 indicating the presence of the signal of thethird wavelength, . . . , and the setting WSn corresponds to data D4 nindicating “update”. Data D4T indicates the total number “y” of dataeach indicating “update” or “presence” out of the data D41 to D4 n.

The fourth (bottom) row shown in FIG. 6 represents final wavelengthnumber information which has undergone the processing shown in the thirdrow to be transmitted to the downstream device (wavelength demultiplexer102). That is, to the downstream device is transmitted wavelength numberinformation including data D51 indicating the presence of the controlledoptical signal of the wavelength λ1, data D52 indicating the absence ofthe signal of the wavelength λ2, data D53 indicating the presence of thesignal of the wavelength λ3, . . . , data D5 n indicating the presenceof the signal of the wavelength λn, and data D5T indicating the totalnumber “y” of data each indicating the presence of a controlled opticalsignal out of the data D51 to D5 n.

In the following, a description will be made in detail of the operationof the wavelength demultiplexer 102.

In the wavelength demultiplexer 102, the wavelength demultiplexingsection 4-2 separates a wavelength number information signal from thereceived WDM optical signal S2 to send it to the wavelength numberinformation managing section 3-3.

The wavelength number information managing section 3-3 feeds thewavelength demultiplexing section 4-2 with information on the totalnumber of wavelengths obtained from the received optical signal.

The aforementioned operation of the respective devices will be describedwith reference to flowcharts.

FIG. 7 is a flowchart showing the operation of the wavelengthmultiplexer 100 depicted in FIG. 4 for processing a wavelength numberinformation signal. FIG. 8 is a flowchart showing the operation of theoptical repeater 101 depicted in FIG. 4 for processing the wavelengthnumber information signal. FIG. 9 is a flowchart showing the operationof the wavelength demultiplexer 102 depicted in FIG. 4 for processingthe wavelength number information signal.

Referring to FIG. 7, the wavelength multiplexer 100 (see FIG. 4)determines whether or not the optical signal level is equal to or morethan a reference value at the input section (ports P11 to P1 n) of thewavelength multiplexing section 2-1 (step S1).

When having determined that the optical signal level is not less thanthe reference value (step S1/Y), the wavelength multiplexer 100 setswavelength number information to indicate the “presence” of the opticalsignal of the relevant wavelength (step S2). On the other hand, whenhaving determined that the optical signal level is less than thereference value (step S1/N), the wavelength multiplexer 100 sets thewavelength number information to indicate the “absence” of the opticalsignal of the relevant wavelength (step S3).

The wavelength number information managing section 3-1 counts dataindicating the “presence” of an optical signal, thereby informing thewavelength multiplexing section 2-1 of the total number of wavelengths(step S4).

The wavelength multiplexing section 2-1 multiplexes a wavelength numberinformation signal generated in the wavelength number informationmanaging section 3-1 together with optical signals of other wavelengths,and transmits a WDM optical signal to the downstream device: the opticalrepeater 101 (step S5).

Referring to FIG. 8, the optical repeater 101 (see FIG. 4) separates thewavelength number information signal from the received WDM opticalsignal in the wavelength demultiplexing section 4-1 to send it to thewavelength number information managing section 3-2 (step T1).

The wavelength number information managing section 3-2 feeds thewavelength demultiplexing section 4-1 with information on the totalnumber of wavelengths obtained from the wavelength number informationsignal (step T2).

The wavelength number information managing section 3-2 determineswhether or not an external setting with respect to each wavelengthindicates “terminate” (step T3), this step corresponding to the process5 described hereinbefore. When having determined that the externalsetting indicates “terminate” (step T3/Y), the wavelength numberinformation managing section 3-2 determines whether or not the opticalsignal level at the input section (ports P31 to P3 n) of the wavelengthmultiplexing section 2-2 is equal to or more than a reference value(step T4).

When having determined that the optical signal level is not less thanthe reference value (step T4/Y), the wavelength number informationmanaging section 3-2 sets wavelength number information to indicate the“presence” of the optical signal of the relevant wavelength (step T5).On the other hand, when having determined that the optical signal levelis less than the reference value (step T4/N), the wavelength numberinformation managing section 3-2 sets the wavelength number informationto indicate the “absence” of the optical signal of the relevantwavelength (step T11).

After that, the wavelength number information managing section 3-2counts data each indicating the “presence” of an optical signal, therebyinforming the wavelength multiplexing section 2-2 of the total number ofwavelengths (step T6).

The wavelength multiplexing section 2-2 multiplexes a wavelength numberinformation signal generated in the wavelength number informationmanaging section 3-2 together with optical signals of other wavelengths,and transmits a WDM optical signal to the downstream device: thewavelength demultiplexer 102 (step T7).

In step T3, when having determined that the external setting for awavelength does not indicate “terminate” (step T3/N=“pass”), thewavelength number information managing section 3-2 also determineswhether or not the optical signal level at the input section of thewavelength multiplexing section 2-2 is equal to or more than a referencevalue (step T8). When having determined that the optical signal level isnot less than the reference value (step T8/Y), the wavelength numberinformation managing section 3-2 determines whether or not thewavelength number information contained in the received wavelengthnumber information signal indicates the “presence” of the optical signalof the wavelength (step T9). When having determined that the wavelengthnumber information indicates the “presence” of the optical signal (stepT9/Y), the wavelength number information managing section 3-2 sets thewavelength number information to indicate the “presence” of the opticalsignal of the relevant wavelength (step T5). Thereafter, steps T6 and T7are performed.

When having determined that the optical signal level is less than thereference value (step T8/N), and that the wavelength number informationcontained in the received wavelength number information signal does notindicate the “presence” of the optical signal (step T9/N), thewavelength number information managing section 3-2 sets the wavelengthnumber information to indicate the “absence” of the optical signal ofthe relevant wavelength (step T10). Thereafter, steps T6 and T7 areperformed.

Referring to FIG. 9, the wavelength demultiplexer 102 (see FIG. 4)separates the wavelength number information signal from the received WDMoptical signal in the wavelength demultiplexing section 4-2 to send itto the wavelength number information managing section 3-3 (step U1).

The wavelength number information managing section 3-3 feeds thewavelength demultiplexing section 4-2 with information on the totalnumber of wavelengths obtained from the wavelength number informationsignal (step U2).

Incidentally, examples of devices of this kind include an opticalrepeater (amplifier) that adjusts the level of a WDM optical signalwithout wavelength-division multiplexing optical signals. Such anoptical amplifier repeater has a construction without the wavelengthnumber information managing section, and operates similarly to theoptical repeater 101 except not to perform wavelength-divisionmultiplexing on optical signals. The optical amplifier repeater alsoadjusts the signal level based on wavelength number information.However, since the optical amplifier repeater does not demultiplex a WDMoptical signal and wavelength-division multiplexes a wavelength numberinformation signal only, it does not need wavelength number informationabout individual wavelengths as described above. Although the opticalamplifier repeater controls controlled optical signals based on thetotal number of wavelengths at present, it may control the signals basedon the total number of data each indicating the “presence” of acontrolled optical signal

Generally, repetitive multiplexing and demultiplexing on a WDM opticalsignal cause optical noise, which tends to increase the optical level ofa wavelength at which originally no optical signal is present. However,according to the first embodiment of the present invention, wavelengthnumber information can be precisely transmitted from an upstream deviceto a downstream device. Therefore, by application of the WDM opticalsignal transmission method of this embodiment, it is possible todistinguish correctly between optical level caused by optical noise andthat of a main signal.

Second Embodiment

FIG. 10 is a schematic diagram showing a wavelength division multiplexedoptical signal transmission system to which is applied a wavelengthdivision multiplexed optical signal transmission method according to thesecond embodiment of the present invention.

As can be seen in FIG. 10, the WDM optical signal transmission system ofthis embodiment is a ring network system comprising optical repeaters101-1, 101-2 and 101-3 only.

The ring network has a construction in which devices are arranged toform a circle. In this construction, optical signals are transmittedfrom one device to another with wavelengths λ1 to λn. Each device needsto have functions for demultiplexing a WDM optical signal input theretointo optical signals of respective wavelengths λ1 to λn, determiningwhether to drop, add or pass through an optical signal with respect toeach wavelength, and multiplexing the optical signals into a WDM opticalsignal to transmit it. The optical repeater 101 can implement thefunctions.

Besides, a device that terminates wavelength number information isessential for this system to prevent the information from looping. Inthis device, external settings for all wavelengths indicate “terminate”,and the wavelength repeating section 5-1 is necessarily utilized for apassing optical signal.

Incidentally, while the WDM optical signal transmission system of thisembodiment comprises three optical repeaters 101-1, 101-2 and 101-3,there is no special limitation on the number of optical repeaters.

In FIG. 10, the optical repeater 101-1 at left is the device thatterminates wavelength number information, and the symbols “※” indicatesa connection therebetween. The optical repeater 101-1 at left providesthe upstream device as well as the downstream device.

Incidentally, examples of devices of this kind include an opticalrepeater (amplifier) that adjusts the level of a WDM optical signalwithout wavelength-division multiplexing optical signals. Such anoptical amplifier repeater has a construction without the wavelengthnumber information managing section, and operates similarly to therespective optical repeaters 101-1, 101-2 and 101-3 except not toperform wavelength-division multiplexing on optical signals. The opticalamplifier repeater also adjusts the signal level based on wavelengthnumber information. However, since the optical amplifier repeater doesnot demultiplex a WDM optical signal and wavelength-division multiplexesa wavelength number information signal only, it does not need wavelengthnumber information about individual wavelengths as described above.Although the optical amplifier repeater controls controlled opticalsignals based on the total number of wavelengths at present, it maycontrol the signals based on the total number of data each indicatingthe “presence” of a controlled optical signal

As is described above, according to the second embodiment of the presentinvention, the WDM optical signal transmission system may be constructedof optical repeaters and optical fibers. In addition, wavelength numberinformation can be precisely transmitted from an upstream device to adownstream device, and therefore, it is possible to distinguishcorrectly between optical level caused by optical noise and that of amain signal.

Third Embodiment

FIG. 11(a) is a schematic diagram showing a wavelength divisionmultiplexed optical signal transmission system to which is applied awavelength division multiplexed optical signal transmission methodaccording to the third embodiment of the present invention. FIG. 11(b)is a schematic diagram showing an optical repeater depicted in FIG.11(a).

As can be seen in FIG. 11(a), the WDM optical signal transmission systemof this embodiment comprises a plurality of optical repeaters 80-1 to80-4 connected via plural pairs of optical fibers 7-1 a and 7-1 b to 7-4a and 7-4 b. While FIG. 11(a) shows four optical repeaters connected viafour pairs of optical fibers, there is no special limitation on thenumber of optical repeaters as well as pairs of optical fibers.

The optical repeater 80-1 includes a pair of optical repeater units101-1 and 101-2. As shown in FIG. 11(b), both the optical repeater units101-1 and 101-2 has the same construction as described previously forthe optical repeater 101 in connection with FIG. 4. The optical repeaterunits 101-1 and 101-2 are arranged so as to receive WDM optical signalsfrom opposite directions as well as outputting them to oppositedirections.

The other optical repeaters 80-2 to 80-4 are of the same construction asthe optical repeater 80-1.

In the WDM optical signal transmission system of this embodiment, forexample, a controlled optical signal having a wavelength λ1 may be inputto the external interface signal receiving section 1-3 of the opticalrepeater 80-1 and output from the external interface signal transmittingsection 6-2 of the optical repeater 80-2. Similarly, a controlledoptical signal having a wavelength λ2 may be input to the externalinterface signal receiving section 1-3 of the optical repeater 80-2 andoutput from the external interface signal transmitting section 6-2 ofthe optical repeater 80-3. In other words, any controlled optical signalinput to the external interface signal receiving section 1-3 of any oneof the optical repeaters 80-1 to 80-4 may be output from the externalinterface signal transmitting section 6-2 of any one of the repeaters80-1 to 80-4.

As is described above, according to the third embodiment of the presentinvention, the WDM optical signal transmission system has an independentfunctional block and performs independent processing with respect to onedirection. That is, the combination of the optical repeaters each havinga pair of optical repeater units enables the WDM optical signaltransmission system to be applicable to a bidirectional communicationnetwork.

Fourth Embodiment

FIG. 12 is a schematic diagram showing a wavelength division multiplexedoptical signal transmission system to which is applied a wavelengthdivision multiplexed optical signal transmission method according to thefourth embodiment of the present invention.

Referring to FIG. 12, the WDM optical signal transmission system of thisembodiment comprises a plurality of optical repeaters 80-1 each having apair of optical repeater units. Ones of the repeater unit pairs in therespective optical repeaters are connected by optical fibers to form astraight transmission line, and the others are also connected by opticalfibers to form a straight transmission line. The optical repeater unitsat both ends are connected to an upstream device and a downstreamdevice, respectively.

In the WDM optical signal transmission system of this embodiment, WDMoptical signals each composed of a control optical signal and aplurality of controlled optical signals are transmitted in oppositedirections through the straight transmission lines, respectively.

Each of the optical repeater units includes a demultiplexer fordemultiplexing a WDM optical signal transmitted from an upstream opticalrepeater unit into optical signals each having a different wavelength, aprocessor for processing the controlled optical signals of differentwavelengths individually based on the control optical signal thatcontains wavelength number information indicating the presence orabsence of a controlled optical signal with respect to each wavelength,and a multiplexer for remultiplexing the control optical signal and thecontrolled optical signals that have undergone the processing by theprocessor.

Namely, the WDM optical signal transmission system of this embodimentcomprises a plurality of the optical repeaters 80-1 as shown in FIG.11(b), which are connected by optical fibers so as to form straighttransmission lines. Both ends of each transmission line are connected tothe wavelength multiplexer 100 and the wavelength demultiplexer 102,respectively.

As is described above, according to the fourth embodiment of the presentinvention, the WDM optical signal transmission system has an independentfunctional block and performs independent processing with respect to onedirection. That is, the combination of the optical repeaters each havinga pair of optical repeater units enables the WDM optical signaltransmission system to be applicable to a bidirectional communicationnetwork.

As set forth hereinabove, in accordance with the present invention,since the wavelength number information indicates the presence orabsence of an optical signal for each wavelength individually, thenumber of wavelengths can be detected without error even when opticalnoise is caused in an optical repeater, and also such functions asadjustment and monitoring of the level of a wavelength divisionmultiplexed optical signal are performed properly.

While the present invention has been described with reference to theparticular illustrative embodiments, it is not to be restricted by theembodiments but only by the appended claims. It is to be appreciatedthat those skilled in the art can change or modify the embodimentswithout departing from the scope and spirit of the present invention.

1. A wavelength division multiplexed optical signal transmission methodfor transmitting via one or more optical repeaters a wavelength divisionmultiplexed optical signal composed of a control optical signal and aplurality of controlled optical signals from an upstream device to adownstream device through optical fibers, the method comprising thesteps of: in the optical repeater, demultiplexing a wavelength divisionmultiplexed optical signal transmitted from the upstream device intooptical signals each having a different wavelength; processing thecontrolled optical signals of different wavelengths individually basedon the control optical signal that contains wavelength numberinformation indicating the presence or absence of a controlled opticalsignal with respect to each wavelength; remultiplexing the controloptical signal and the controlled optical signals that have undergonethe processing to obtain a wavelength division multiplexed opticalsignal; and transmitting the wavelength division multiplexed opticalsignal to the downstream device.
 2. The wavelength division multiplexedoptical signal transmission method claimed in claim 1, wherein: in thecase where the wavelength number information provides a signal presentindication corresponding to a controlled optical signal, when the signalhas not deteriorated, the optical repeater allows the signal to passthrough without changing the signal present indication of the wavelengthnumber information, while, when the signal has deteriorated, the opticalrepeater once terminates the signal and regenerates a controlled opticalsignal to allow the new signal regenerated from the deteriorated signalto pass through without changing the signal present indication of thewavelength number information; and in the case where the wavelengthnumber information provides a signal absent indication corresponding toa controlled optical signal, when receiving an optical signal from theoutside, the optical repeater outputs the optical signal as thecontrolled optical signal and updates the wavelength number informationto indicate the presence of the signal, while, when receiving no opticalsignal from the outside, the optical repeater terminates the controlledoptical signal without changing the signal absent indication of thewavelength number information.
 3. The wavelength division multiplexedoptical signal transmission method claimed in claim 1, wherein theoptical repeater controls functions for adjustment and monitoring of thelevel of a wavelength division multiplexed optical signal input theretobased on the wavelength number information from the control opticalsignal.
 4. The wavelength division multiplexed optical signaltransmission method claimed in claim 1, wherein the wavelength numberinformation includes information on the number of multiplexedwavelengths.
 5. A wavelength division multiplexed optical signaltransmission method in which a plurality of optical repeaters connectedin a ring by optical fibers transmit a wavelength division multiplexedoptical signal composed of a control optical signal and a plurality ofcontrolled optical signals from one to another in one direction, themethod comprising the steps of: in the optical repeater, demultiplexinga wavelength division multiplexed optical signal transmitted from anupstream optical repeater into optical signals each having a differentwavelength; processing the controlled optical signals of differentwavelengths individually based on the control optical signal thatcontains wavelength number information indicating the presence orabsence of a controlled optical signal with respect to each wavelength;remultiplexing the control optical signal and the controlled opticalsignals that have undergone the processing to obtain a wavelengthdivision multiplexed optical signal; and transmitting the wavelengthdivision multiplexed optical signal to a downstream optical repeater. 6.A wavelength division multiplexed optical signal transmission method fortransmitting wavelength division multiplexed optical signals eachcomposed of a control optical signal and a plurality of controlledoptical signals in opposite directions through transmission lines by aplurality of optical repeaters each having a pair of optical repeaterunits, ones of the repeater unit pairs in the respective opticalrepeaters being connected by optical fibers to form a ring transmissionline and the others also being connected by optical fibers to form aring transmission line, or ones of the repeater unit pairs in therespective optical repeaters being connected by optical fibers to form astraight transmission line, the others also being connected by opticalfibers to form a straight transmission line and optical repeater unitsat both ends being connected to an upstream device and a downstreamdevice, respectively, the method comprising the steps of: in the opticalrepeater unit, demultiplexing a wavelength division multiplexed opticalsignal transmitted from an upstream optical repeater unit into opticalsignals each having a different wavelength; processing the controlledoptical signals of different wavelengths individually based on thecontrol optical signal that contains wavelength number informationindicating the presence or absence of a controlled optical signal withrespect to each wavelength; remultiplexing the control optical signaland the controlled optical signals that have undergone the processing toobtain a wavelength division multiplexed optical signal; andtransmitting the wavelength division multiplexed optical signal to adownstream optical repeater unit.
 7. The wavelength division multiplexedoptical signal transmission method claimed in claim 6, wherein: in thecase where the wavelength number information provides a signal presentindication corresponding to a controlled optical signal, when the signalhas not deteriorated, the optical repeater unit allows the signal topass through without changing the signal present indication of thewavelength number information, while, when the signal has deteriorated,the optical repeater unit once terminates the signal and regenerates acontrolled optical signal to allow the new signal regenerated from thedeteriorated signal to pass through without changing the signal presentindication of the wavelength number information; and in the case wherethe wavelength number information provides a signal absent indicationcorresponding to a controlled optical signal, when receiving an opticalsignal from the outside, the optical repeater unit outputs the opticalsignal as the controlled optical signal and updates the wavelengthnumber information to indicate the presence of the signal, while, whenreceiving no optical signal from the outside, the optical repeater unitterminates the controlled optical signal without changing the signalabsent indication of the wavelength number information.
 8. Thewavelength division multiplexed optical signal transmission methodclaimed in claim 6, wherein the optical repeater unit controls functionsfor adjustment and monitoring of the level of a wavelength divisionmultiplexed optical signal input thereto based on the wavelength numberinformation from the control optical signal.
 9. A wavelength divisionmultiplexed optical signal transmission system comprising an upstreamdevice, one or more optical repeaters and a downstream device fortransmitting via the optical repeater a wavelength division multiplexedoptical signal composed of a control optical signal and a plurality ofcontrolled optical signals from the upstream device to the downstreamdevice through optical fibers, wherein: the upstream device includes areceiver for receiving a control optical signal and controlled opticalsignals and a multiplexer for multiplexing the control optical signaland the controlled optical signals received by the receiver; the opticalrepeater includes a demultiplexer for demultiplexing a wavelengthdivision multiplexed optical signal transmitted from the upstream deviceinto optical signals each having a different wavelength, a processor forprocessing the controlled optical signals of different wavelengthsindividually based on the control optical signal that containswavelength number information indicating the presence or absence of acontrolled optical signal with respect to each wavelength, and amultiplexer for remultiplexing the control optical signal and thecontrolled optical signals; and the downstream device includes ademultiplexer for demultiplexing a wavelength division multiplexedoptical signal transmitted from the optical repeater and a transmitterfor transmitting a control optical signal and controlled optical signalsobtained by demultiplexing the wavelength division multiplexed opticalsignal to the outside.
 10. The wavelength division multiplexed opticalsignal transmission system claimed in claim 9, wherein: in the casewhere the wavelength number information provides a signal presentindication corresponding to a controlled optical signal, when the signalhas not deteriorated, the processor of the optical repeater allows thesignal to pass through without changing the signal present indication ofthe wavelength number information, while, when the signal hasdeteriorated, the processor once terminates the signal and regenerates acontrolled optical signal to allow the new signal regenerated from thedeteriorated signal to pass through without changing the signal presentindication of the wavelength number information; and in the case wherethe wavelength number information provides a signal absent indicationcorresponding to a controlled optical signal, when receiving an opticalsignal from the outside, the processor outputs the optical signal as thecontrolled optical signal and updates the wavelength number informationto indicate the presence of the signal, while, when receiving no opticalsignal from the outside, the processor terminates the controlled opticalsignal without changing the signal absent indication of the wavelengthnumber information.
 11. The wavelength division multiplexed opticalsignal transmission system claimed in claim 9, wherein the processor ofthe optical repeater controls functions for adjustment and monitoring ofthe level of a wavelength division multiplexed optical signal inputthereto based on the wavelength number information from the controloptical signal.
 12. The wavelength division multiplexed optical signaltransmission system claimed in claim 9, wherein the wavelength numberinformation includes information on the number of multiplexedwavelengths.
 13. A wavelength division multiplexed optical signaltransmission system comprising a plurality of optical repeatersconnected in a ring by optical fibers which transmit a wavelengthdivision multiplexed optical signal composed of a control optical signaland a plurality of controlled optical signals from one to another in onedirection, wherein the optical repeater includes a demultiplexer fordemultiplexing a wavelength division multiplexed optical signaltransmitted from an upstream optical repeater into optical signals eachhaving a different wavelength, a processor for processing the controlledoptical signals of different wavelengths individually based on thecontrol optical signal that contains wavelength number informationindicating the presence or absence of a controlled optical signal withrespect to each wavelength, and a multiplexer for remultiplexing thecontrol optical signal and the controlled optical signals to transmit awavelength division multiplexed optical signal to a downstream opticalrepeater.
 14. A wavelength division multiplexed optical signaltransmission system comprising a plurality of optical repeaters eachhaving a pair of optical repeater units which transmit wavelengthdivision multiplexed optical signals each composed of a control opticalsignal and a plurality of controlled optical signals in oppositedirections through transmission lines, wherein: ones of the repeaterunit pairs in the respective optical repeaters are connected by opticalfibers to form a ring transmission line, and the others are alsoconnected by optical fibers to form a ring transmission line; or ones ofthe repeater unit pairs in the respective optical repeaters areconnected by optical fibers to form a straight transmission line, theothers are also connected by optical fibers to form a straighttransmission line, and optical repeater units at both ends are connectedto an upstream device and a downstream device, respectively; and theoptical repeater unit includes: a demultiplexer for demultiplexing awavelength division multiplexed optical signal transmitted from anupstream optical repeater unit into optical signals each having adifferent wavelength; a processor for processing the controlled opticalsignals of different wavelengths individually based on the controloptical signal that contains wavelength number information indicatingthe presence or absence of a controlled optical signal with respect toeach wavelength; and a multiplexer for remultiplexing the controloptical signal and the controlled optical signals that have undergonethe processing by the processor.
 15. The wavelength division multiplexedoptical signal transmission system claimed in claim 14, wherein: in thecase where the wavelength number information provides a signal presentindication corresponding to a controlled optical signal, when the signalhas not deteriorated, the processor of the optical repeater unit allowsthe signal to pass through without changing the signal presentindication of the wavelength number information, while, when the signalhas deteriorated, the processor once terminates the signal andregenerates a controlled optical signal to allow the new signalregenerated from the deteriorated signal to pass through withoutchanging the signal present indication of the wavelength numberinformation; and in the case where the wavelength number informationprovides a signal absent indication corresponding to a controlledoptical signal, when receiving an optical signal from the outside, theprocessor outputs the optical signal as the controlled optical signaland updates the wavelength number information to indicate the presenceof the signal, while, when receiving no optical signal from the outside,the processor terminates the controlled optical signal without changingthe signal absent indication of the wavelength number information. 16.The wavelength division multiplexed optical signal transmission systemclaimed in claim 14, wherein the processor of the optical repeater unitcontrols functions for adjustment and monitoring of the level of awavelength division multiplexed optical signal input thereto based onthe wavelength number information from the control optical signal. 17.An optical repeater for transmitting a wavelength division multiplexedoptical signal composed of a control optical signal and a plurality ofcontrolled optical signals from the upstream device to the downstreamdevice through optical fibers, the optical repeater comprising: ademultiplexer for demultiplexing a wavelength division multiplexedoptical signal transmitted from the upstream device into optical signalseach having a different wavelength; a processor for processing thecontrolled optical signals of different wavelengths individually basedon the control optical signal that contains wavelength numberinformation indicating the presence or absence of a controlled opticalsignal with respect to each wavelength; and a multiplexer forremultiplexing the control optical signal and the controlled opticalsignals.
 18. The optical repeater claimed in claim 17, wherein: in thecase where the wavelength number information provides a signal presentindication corresponding to a controlled optical signal, when the signalhas not deteriorated, the processor of the optical repeater allows thesignal to pass through without changing the signal present indication ofthe wavelength number information, while, when the signal hasdeteriorated, the processor once terminates the signal and regenerates acontrolled optical signal to allow the new signal regenerated from thedeteriorated signal to pass through without changing the signal presentindication of the wavelength number information; and in the case wherethe wavelength number information provides a signal absent indicationcorresponding to a controlled optical signal, when receiving an opticalsignal from the outside, the processor outputs the optical signal as thecontrolled optical signal and updates the wavelength number informationto indicate the presence of the signal, while, when receiving no opticalsignal from the outside, the processor terminates the controlled opticalsignal without changing the signal absent indication of the wavelengthnumber information.
 19. The optical repeater claimed in claim 17,wherein the processor of the optical repeater controls functions foradjustment and monitoring of the level of a wavelength divisionmultiplexed optical signal input thereto based on the wavelength numberinformation from the control optical signal.
 20. The optical repeaterclaimed in claim 17, wherein the wavelength number information includesinformation on the number of multiplexed wavelengths.
 21. An opticalrepeater applied to a wavelength division multiplexed optical signaltransmission system comprising a plurality of the optical repeatersconnected in a ring by optical fibers which transmit a wavelengthdivision multiplexed optical signal composed of a control optical signaland a plurality of controlled optical signals from one to another in onedirection, the optical repeater comprising: a demultiplexer fordemultiplexing a wavelength division multiplexed optical signaltransmitted from an upstream optical repeater into optical signals eachhaving a different wavelength; a processor for processing the controlledoptical signals of different wavelengths individually based on thecontrol optical signal that contains wavelength number informationindicating the presence or absence of a controlled optical signal withrespect to each wavelength; and a multiplexer for remultiplexing thecontrol optical signal and the controlled optical signals to transmit awavelength division multiplexed optical signal to a downstream opticalrepeater.
 22. An optical repeater applied to a wavelength divisionmultiplexed optical signal transmission system comprising a plurality ofthe optical repeaters each having a pair of optical repeater units whichtransmit wavelength division multiplexed optical signals each composedof a control optical signal and a plurality of controlled opticalsignals in opposite directions through transmission lines, wherein: onesof the repeater unit pairs in the respective optical repeaters areconnected by optical fibers to form a ring transmission line, and theothers are also connected by optical fibers to form a ring transmissionline; or ones of the repeater unit pairs in the respective opticalrepeaters are connected by optical fibers to form a straighttransmission line, the others are also connected by optical fibers toform a straight transmission line, and optical repeater units at bothends are connected to an upstream device and a downstream device,respectively; and the optical repeater unit includes: a demultiplexerfor demultiplexing a wavelength division multiplexed optical signaltransmitted from an upstream optical repeater unit into optical signalseach having a different wavelength; a processor for processing thecontrolled optical signals of different wavelengths individually basedon the control optical signal that contains wavelength numberinformation indicating the presence or absence of a controlled opticalsignal with respect to each wavelength; and a multiplexer forremultiplexing the control optical signal and the controlled opticalsignals that have undergone the processing by the processor.
 23. Theoptical repeater claimed in claim 22, wherein: in the case where thewavelength number information provides a signal present indicationcorresponding to a controlled optical signal, when the signal has notdeteriorated, the processor of the optical repeater unit allows thesignal to pass through without changing the signal present indication ofthe wavelength number information, while, when the signal hasdeteriorated, the processor once terminates the signal and regenerates acontrolled optical signal to allow the new signal regenerated from thedeteriorated signal to pass through without changing the signal presentindication of the wavelength number information; and in the case wherethe wavelength number information provides a signal absent indicationcorresponding to a controlled optical signal, when receiving an opticalsignal from the outside, the processor outputs the optical signal as thecontrolled optical signal and updates the wavelength number informationto indicate the presence of the signal, while, when receiving no opticalsignal from the outside, the processor terminates the controlled opticalsignal without changing the signal absent indication of the wavelengthnumber information.
 24. The optical repeater claimed in claim 22,wherein the processor of the optical repeater unit controls functionsfor adjustment and monitoring of the level of a wavelength divisionmultiplexed optical signal input thereto based on the wavelength numberinformation from the control optical signal.